Anti-cavitation and overload relief valve for a hydraulic system

ABSTRACT

A hydraulic system including at least one hydraulic cylinder is provided with an anti-cavitation and overload relief valve having a housing, a first chamber within the housing in fluid communication with one end of the cylinder, and a second chamber within the housing in fluid communication with a fluid reservoir. A fluid passageway within the valve housing connects the first and second chambers. A movable valve assembly is positioned within the fluid passageway for operating in a plurality of modes for providing anti-cavitation and overload relief. The valve includes a stationary portion positioned within the fluid passageway between the first and second chambers having a valve seat. The movable valve assembly includes a poppet mechanism for sealingly engaging a valve seat of the movable valve element when the movable valve assembly is operating in first and third modes. A tang on the head of the poppet engages a reduced diameter portion of the stationary valve element in order to maintain fluid communication between the first and second chambers during the second mode of operation. An axial extension of a poppet spring seat limits the travel of the movable valve during the third mode of operation and limits the stress on a poppet spring.

This is a continuation in part of my U.S. application, Ser. No. 879,026,filed Feb. 17, 1978 now U.S. Pat. No. 4,210,170.

BACKGROUND OF THE INVENTION

The present invention relates generally to hydraulic valves for use influid pressure operated systems and more particularly to hydraulicvalves for the relief of both abnormally high and abnormally lowpressure conditions in such systems.

A common problem in hydraulic circuits has been the provision of highpressure protection devices for venting fluid to a reservoir where thecircuit is subjected to a higher pressure level than desired. Manydevices have been utilized in the prior art for high pressureprotection. Generally, these devices can be classified as either (1)direct-acting, utilizing a poppet loaded directly against a spring, or(2) pilot-operated, utilizing a poppet loaded by a reference pressure.

In addition to high pressure protection, the need has also existed forprotection against abnormally low pressure conditions which result incavitation. This condition exists when fluid leaves one side of ahydraulic cylinder and is not replaced at an equal rate on the oppositeside. A known solution to the cavitation problem is the use of a one-waycheck valve which permits fluid to enter the voided cylinder from areservoir and simultaneously prevents fluid from leaving the cylinderunder pressure.

Therefore, complete protection of a hydraulic cylinder requires bothhigh pressure protection and cavitation prevention on both cylinderends. Combination valve assemblies providing both high and low pressureprotection within a single package are also well known in the art.However, to date such combination assemblies have not performed as wellas individual valve units due to the following problems: (1) To date,such combination valve assemblies have had to rely in part on dynamicsealing. The resulting seal friction has interfered with the performanceof these valves. (2) Undue passageway restrictions, and (3) otherproblems resulting from limitations on the size of the valve packagehave limited performance.

SUMMARY OF THE INVENTION

Accordingly, a hydraulic system is provided with an anti-cavitation andoverload relief valve having a housing, a first chamber within thehousing in fluid communication with one end of the cylinder, and asecond chamber within the housing in fluid communication with a fluidreservoir. A fluid passageway within the valve housing connects thefirst and second chambers. A movable valve assembly is positioned withinthe fluid passageway for operating in a first mode to block fluid flowbetween the first and second chambers, for operating in a second mode topermit fluid flow from the first chamber to the second chamber only whenthe pressure in the first chamber exceeds the pressure in the secondchamber by a first predetermined amount, and for operating in a thirdmode to permit fluid flow from the second chamber to the first chamberonly when the pressure in the second chamber exceeds the pressure in thefirst chamber by a second predetermined amount. The valve includes astationary portion positioned within the fluid passageway between thefirst and second chambers having a valve seat. The movable valveassembly includes a movable valve element having a sealing portion forengaging the valve seat of the stationary portion when the movable valveassembly is operating in the first and second modes. The movable valveassembly further has a valve seat and a poppet mechanism is provided forsealingly engaging the valve seat of the movable valve element when themovable valve assembly is operating in the first and third modes.

The poppet mechanism has features which enhance the operation of thevalve and increase its longevity. In particular, the poppet issubstantially solid in cross-section, has a head located at one end, astem adjacent the head, and a spring seat fixed to the end of the stem.A tang axially projects from the head and is engaged by a reduceddiameter portion of the stationary portion of the valve. The tangfeature reduces restriction of fluid communication between the first andsecond chambers when the invention is operating in its second mode, thusenhancing the performance of the valve. The life of the valve isincreased by a poppet spring stress reducing feature. The latter isprovided by the first spring seat of the poppet. The seat has a radiallyprojecting body portion for keeping the first poppet spring between thefirst seat and the movable valve element. The stress on that spring isreduced by an axially extending body portion of the spring seat whichlimits the travel of the movable valve element. Hence, the first poppetspring is prevented from experiencing overstress, thereby contributingto the longevity of the invention. In order to reduce costs, the springseat can be welded or press fit to the stem of the poppet.

OBJECTS OF THE INVENTION

An object of the present invention is the provision of a compact directacting hydraulic valve for overload relief and cavitation protection ofa hydraulic cylinder.

Another object of the present invention is the provision of ananti-cavitation and overload relief valve which exhibits low leakageproperties without the use of dynamic seals.

A further object of the present invention is the provision of ananti-cavitation and overload relief valve which maintains pressurerelatively constant as flow increases through the valve.

Still another object of the present invention is to minimize the stresson the components of an anti-cavitation and overload relief valve.

Still another object of the present invention is to simplify themanufacture of an anti-cavitation and overload relief valve.

Other objects, advantages, and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a hydraulic system employing the hydraulic valve of thepresent invention, with the valve shown in partial longitudinal crosssection in a first operating mode.

FIG. 2 shows the hydraulic valve shown in FIG. 1 in a second operatingmode.

FIG. 3 shows the hydraulic valve shown in FIG. 1 in a third operatingmode.

FIG. 4 shows an alternate embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 shows a hydraulic overload relief and anti-cavitation protectionsystem for hydraulic equipment such as is found on a loader 10. Theloader includes a plurality of hydraulic cylinders 12 with each end ofeach cylinder being connected to a hydraulic valve 20 of the presentinvention. For ease of illustration, only one such valve 20 has beenillustrated in detail.

Each valve 20 includes a housing 22 which, typically, is also thehousing for other valves utilized in the control of the hydraulicequipment. Each housing includes a first chamber 24 in fluidcommunication with one end of a hydraulic cylinder 12. Each housing 22further includes a second chamber 26 in fluid communication with areservoir, graphically illustrated at 28. Extending longitudinally theentire length of the valve is a central fluid passageway 30 whichconnects the first chamber 24 with the second chamber 26. A movablevalve assembly, the operation of which will be described later, iscontained entirely within the fluid passageway 30.

The movable valve assembly includes a movable valve element 32 having anouter surface 34 in sliding engagement with the fluid passageway 30 anda tapered sealing surface 36 on one end thereof. The movable valveelement 32 further includes a hollow interior which is symmetrical aboutaxis 38 and includes a first portion 40 axially adjacent the tapered end36. A second interior portion 42 is axially adjacent to the firstinterior portion 40 and has a diameter that is smaller than the diameterof the interior portion 40. The joint 44 between the first interiorportion 40 and the second interior portion 42 defines a valve seat 44.The interior of the movable valve element 32 further includes a thirdportion 46 axially adjacent to the portion 42 and having a diameterwhich is smaller than the diameter of the portion 42. The movable valveelement 32 further includes a plurality of holes 48 in the outer wallsurrounding the interior portion 42, for permitting fluid communicationbetween the chamber 24 and the interior portion 42. The movable valveelement 32 further includes a spring seat 50 projecting radiallyoutwardly therefrom. The spring seat 50 includes a plurality of slots 52therethrough to permit fluid communication along the passageway 30.

The movable valve assembly further includes a poppet mechanism having apoppet generally indicated at 54 which is substantially solid incross-section and is substantially symmetrically disposed about the axis38. The poppet 54 includes a head 56 at one end and a body portion 58located axially adjacent the head 56 and having a diameter which issmaller than the diameter of the head 56. A tapered sealing portion 60is axially adjacent the body portion 58 and is adapted to sealinglyengage the valve seat 44 on movable valve element 32. The poppet 54further includes a cylindrical stem 62 axially adjacent the taperedsealing portion 60. The cylinderical stem 62 is surrounded by theinterior portion 46 of movable valve element 32 and is in slidingengagement therewith. The head 56 of poppet 54 includes a slot 64 formaintaining fluid communication between the chamber 24 and the chamber26 after the poppet has reached its limit of travel. This function willbecome apparent in the discussion of the operation of the valve whichfollows.

The poppet mechanism further includes a spring seat 66 projectingradially outwardly from the stem 62. The seat 66 may be fastened to thestem 62 by any suitable means and in the preferred embodiment isthreadingly engaged therewith. Accordingly, a lock nut 68 is provided toprevent any undesired rotation between the stem 62 and the spring seat66. A biasing spring 70 is seated on one end against the end surface 72of passageway 30 and is seated at the other end against one side of thespring seat 66. A second biasing spring 74 is positioned between thespring seat 50 and the other side of the spring seat 66. For reasonswhich will become apparent later the force transmitted by the spring 70is less than the force transmitted by the spring 74. The spring seat 66also includes slots 76 to permit fluid communication along the entirelength of fluid passageway 30.

A stationary valve element 78 is positioned within the fluid passageway30 and includes a portion thereof between chambers 24 and 26. Thestationary valve element 78 may be integral with the housing 22, but isillustrated in the preferred embodiment as being threadingly engagedwith the fluid passageway 30. A pair of static seals 80 and 82 andprovided to prevent leakage of hydraulic fluid along the outer surfaceof stationary valve element 78.

The end of 84 of stationary valve element 78 provides a valve seat forthe sealing surface 36 of movable valve element 34. The stationary valveelement 78 includes a hollow interior portion including a portion 86 ofreduced diameter relative to the diameter of valve seat 84. Accordingly,the tapered surface 88 provides a means for limiting the travel of thepoppet 54. The stationary valve element 78 further includes a pluralityof holes 90 for permitting fluid communication between the hollowinterior of the element 78 and chamber 26.

Referring to FIGS. 1 through 3 of the drawings, the operation of thevalve of the present invention will be described in detail. Assumingfirst that the system shown in FIG. 1 is operating normally, that is,the pressure in the end of cylinder 12 to which the valve illustrates isconnected is neither above nor below normal, the movable valve assemblywill be positioned as illustrated in FIG. 1. In this position, sealingsurface 36 is forced into sealing engagement with valve seat 84 by theforce transmitted to the movable valve assembly by spring 70. Likewise,tapered sealing surface 60 of poppet 54 is forced into sealingengagement with valve seat 44 by spring 74. Thus, in this firstoperating mode, fluid flows between chambers 24 and 26 is blocked inboth directions.

Assume next that the pressure in the given cylinder end rises to a firstpredetermined amount which is above that desirable. This could occur,for example, if the boom of the vehicle were being hydraulically drivendownward while the bucket was jammed in a fixed position. In this case,pressure will build up in chamber 24 and be applied against the taperedsurface 60 of poppet 62 until the spring 74 starts to compress, as isillustrated in FIG. 2. The poppet 62 will now be unseated from valveseat 44 and will provide clearance for fluid flow to pass from chamber24 along path 92 to chamber 26. As flow moves along path 92 it appliespressure against face 94 of head 56 and thus increases the compressionload on spring 74. As flow increases, the compression load on spring 74also increases thereby helping to maintain pressure fairly constantrelative to increased flow. Spring 74 will continue to be compresseduntil head 56 abuts tapered surface 88. By providing a limit of travelfor poppet 54, surface 88 prevents overstressing of the poppetmechanism. When the poppet head 56 is in contact with the surface 88,flow path 92 is maintained through slot 64. At this point furtherpressure regulation is sacrificed to prevent further stressing of thepoppet mechanism. It should be noted that since flow path 92 is alongthe outer surface of poppet 54 no dynamic sealing is required. Suchsealing is required when hollow poppets are utilized. Thus, in thesecond mode of operation fluid flow from chamber 24 to chamber 26 ispermitted when the pressure in chamber 24 exceeds the pressure inchamber 26 by a first predetermined amount.

Assume next that the pressure in cavity 26 rises above the pressure incavity 24. When the pressure in cavity 26 rises above the pressure incavity 24 by a predetermined amount, pressure builds up on the head 64and the interior surface 40 of element 34 until poppet 54, movable valveelement 34, spring 74 and spring seat 66 all move in unison to compressspring 70, as is illustrated in FIG. 3. As tapered sealing surface 36 isunseated from valve seat 84, fluid flows from chamber 26 to chamber 24along path 96. Thus, in this third mode of operation fluid flow ispermitted from chamber 26 to chamber 24 only when the pressure in thechamber 26 exceeds the pressure in chamber 24 by a second predeterminedamount.

As is apparent from the above description, it is necessary that thespring 70 transmit less force than the spring 74 so that the operationof the valve is not symmetrical. In other words, the first predeterminedamount referred to above must be considerably greater than the secondpredetermined amount since the valve should remain in the firstoperating mode shown in FIG. 1 throughout normal operation pressures butshould be fairly sensitive to any situation in which the pressure inchamber 26 exceeds the pressure in chamber 24.

Turning to FIG. 4, where like reference numerals refer to like elementsin FIG. 1, there is shown another embodiment of the invention whichincludes several features for enhancing the performance, longevity andcost savings of the invention. To this end, head 56 of poppet 54 isprovided with an axially projection or tang 64'. When the corners oftang 64' engage the tapered surface 88 of stationary valve element 78,the travel of the poppet is stopped. However, a relatively larger openarea around the Head 56 allows greater fluid flow from first chamber 24to second chamber 26 when the valve 20 is in its second mode ofoperation.

In the third mode of operation, movable valve element 34, first spring74 and first spring seat 66' all move in unison to compress secondspring 70. As pressure builds up in chamber 24, first spring 74 iscompressed between valve element 34 and first spring seat 66'. However,that compression is limited by an axially extending body portion 6 offirst spring seat 66', which extends axially from the radial bodyportion 7. Hence, when surface A of interior portion 46 of movable valveelement 32 abuts against surface B of axial body portion 6, the furthertravel of movable valve element 34 is stopped as is the furthercompression of spring 74. A retaining member 68' is either press fit orwelded onto the stem 62 in order to keep the first spring seat 66' onthe stem 68.

Thus, it is apparent that an anti-cavitation and overload reliefprotection system for a hydraulic circuit has been provided which isboth compact and direct action. Furthermore, it is apparent that nodynamic seals are required in the operation of the valve of the presentinvention since flow in either direction is along the outside surface ofthe sealing member. The valve maintains a relatively constant pressureas flow increases over a large operating range. Additionally, the valveincludes means for preventing overstressing of its internal parts.Finally, the construction of the valve of the present invention isrelatively simple and therefore inexpensive.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein, without departing from the invention, and it is, therefore,aimed in the appendant claims to cover all such changes andmodifications as fall within the true spirit and scope of the invention.

What is claimed is:
 1. In a hydraulic valve having a housing; a firstchamber within said housing, adapted to be communicated with a fluidline; a second within said housing, adapted to be communicated with afluid reservoir; a fluid passageway within said housing connecting saidfirst and second chambers; a movable valve assembly positioned withinsaid fluid passageway for operating in a first mode to block fluid flowbetween said first and second chambers, for operating in a second modeto permit fluid flow from said first chamber to said second chamber onlywhen the pressure in said first chamber exceeds the pressure in saidsecond chamber by a first predetermined amount, and for operating in athird mode to permit fluid flow from said second chamber to said firstchamber only when the pressure in said second chamber exceeds thepressure in said first chamber by a second predetermined amount, saidvalve having a stationary portion positioned within said fluidpassageway between said first and second chambers, said stationaryportion including a valve seat; said movable valve assembly including amovable valve element having a sealing portion for engaging said valveseat of said stationary portion when said movable valve assembly isoperating in said first and second modes, said movable valve assemblyfurther having a valve seat, and a poppet mechanism for sealinglyengaging said valve seat of said movable element when said movable valveassembly is operating in said first and third modes, said poppetmechanism including a poppet having a head located at one end thereof, abody portion adjacent said head, a tapered sealing portion adjacent saidbody portion for sealingly engaging said valve seat of said movablevalve element, a stem adjacent said tapered sealing portion, a firstspring seat having a radial portion projecting from the stem of saidpoppet and an axial body portion means extending in the direction of thestem for engaging the movable valve element in order to limit the travelthereof in said third mode when said movable valve means moves relativeto said poppet mechanism.
 2. The invention of claim 1 wherein the firstspring seat is fixedly mounted to said stem.
 3. The invention of claim 2wherein the first spring seat is welded or press fit to the stem.
 4. Theinvention of claim 1, wherein a first spring bias means is seatedbetween one side of said first spring seat and said movable valveelement so as to bias said poppet mechanism against the valve seatincluded in said movable valve element.
 5. The invention of claim 4,wherein a second spring bias means is seated on the other side of saidfirst spring seat so as to bias said movable valve element against thevalve seat included in said staionary portion.
 6. The invention of claim5, wherein the transmitting force of said second spring bias means isless than that of said first spring bias means such that said secondspring bias means compresses before said first spring bias meanscompresses in said third mode.
 7. In a hydraulic overload relief andanti-cavitation protection system for hydraulic equipment having ahydraulic cylinder; a hydraulic valve having a housing; a first chamberwithin said housing in fluid communication with one end of saidhydraulic cylinder; a second chamber within said housing in fluidcommunication with a fluid reservoir; a fluid passageway within saidhousing connecting said first and second chambers; a movable valveassembly positioned within said fluid passageway for operating in afirst mode to block fluid flow between said first and second chambers,for operating in a second mode to permit fluid flow from said firstchamber to said second chamber only when the pressure in said firstchamber exceeds the pressure in said second chamber by a firstpredetermined amount, and for operating in a third mode to permit fluidflow from said second chamber only when the pressure in second chamberexceeds the pressure in said first chamber by a second predeterminedamount; said valve having a stationary portion positioned within saidfluid passageway between said first and second chambers, said stationaryportion including a valve seat; said movable valve assembly including amovable valve element having a sealing portion for engaging said valveseat of said stationary portion when said movable valve assembly isoperating in said first and second modes, said movable valve assemblyfurther having a valve seat, and a poppet mechanism including a poppetfor sealingly engaging said valve seat of said movable valve elementwhen said movable valve assembly is operating in said first and thirdmodes;said poppet mechanism including a poppet which is substantiallysolid in cross-section, has a head located at one end thereof, and atang axially projecting from said head, said tang being comprised of asingle axial projection, said stationary portion further includes atapered reduced diameter portion for engaging the tang of the poppet inorder to limit the travel thereof, whereby said tang intersects saidtapered reduced diameter portion to maintain flow past said taperedportion and through said stationary portion to said second chamber fromsaid first chamber.